ipv6 through SSTP is broken

Recently I tried assigning ipv6 addresses to clients through SSTP server, I use a v6 prefix pool to assign those.

The problem is the first time the client can connect to the server and get an ipv6 address and I can see a route created for the tunnel. But after I disconnect it and reconnect it, it won’t give the client ipv6 address anymore, only LL address exists, and the route isn’t created.

Anyone who have encountered this? RouterOS version is 5.22

ps: ipv4 works like a charm